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United States Patent | 5,193,543 |
Yelderman | March 16, 1993 |
A method and apparatus for non-invasively measuring blood constituent concentration and particularly the oxygen saturation of arterial blood. The apparatus includes at least one light source directed to a tissue area of a patient, such as a finger or earlobe. A photodetector receives emitted light passing through the sample, and a receiver circuit analyzes the data and produces an output which is proportional to the oxygen content of blood. The light source is modulated onto a preselected carrier frequency and the receiver circuit is tuned to the carrier frequency so that undesired signals such as ambient light can be filtered out leaving only the signals created by the emitted light passing through the tissue at the light source frequency. The oxygen content is then calculated using the patient's known red cell count, thereby correcting the final saturation value for patient anemia. Moreover, the calculation for oxygen saturation incorporates red cell scattering parameters for increased accuracy in clinical environments.
Inventors: | Yelderman; Mark (Plano, TX) |
Assignee: | Critikon, Inc. (Tampa, FL) |
Appl. No.: | 865774 |
Filed: | April 6, 1992 |
Current U.S. Class: | 600/310; 356/41 |
Intern'l Class: | A61B 005/02 |
Field of Search: | 128/633,665-666 356/41 |
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Janssen, F. J., "The Principle Design and Features of a New Hb-Oximeter", Medical & Biological Engineering, vol. 10, No. 1, Jan. 1972, pp. 9-22, Pergamon Press. Graf, Rudolf F., Modern Dictionary of Electronics, Howard Sams & Co., Inc., Indianapolis, 3rd Bd., 1970, p. 498. Schmitt, Joseph Michael, "Optical Measurement of Blood Oxygen by Implantable Telemetry", Standard Electronics Laboratories, 31 (Feb. 1986), Technical Report G-558-15, Stanford Electronics Laboratories, Dept. of Electrical Engineering, Stanford University. |
______________________________________ 910 nm 660 nm ______________________________________ .sigma..sub.ao .1340 .0357 .sigma..sub.ar .0802 .3547 .sigma..sub.s 36.34 60.65 .sigma..sub.st .276 .309 .mu. .9924 .9949 ______________________________________